1. Field of the Invention
The invention relates to a photosensitive member for electrophotography used for image formation apparatus in an electrophotographic technology, and more particularly to a photosensitive member for a laser printer comprising a semiconductor laser as a light source.
2. Description of the Prior Art
Recent image formation apparatus in an electrophotographic technology employs a semiconductor laser as a light source, wherein a shortest wave length is 780.about.830 nm for a stable high output in the practically used semiconductor laser. In the meantime, a photosensitive member used in a conventional image formation apparatus or a photosensitive member employing an amorphous silicon not including Ge as photoconductive layer (called hereinafter a-Si) are lower in sensitivity in the range of longer wavelength, so that it is expected to practically use such a photosensitive member employing an amorphous silicon having Ge as photoconductive layer (called hereinafter a-SiGe) with a higher sensitivity in the longer wavelength range.
a-SiGe has such advantages as (1) longer life, (2) harmless to men and (3) highly sensitive to a longer wavelength.
Conventionally, a photoconductive layer of a-Si or a-SiGe is made by the plasma CVD method, the sputtering method or the like. A total content of hydrogen and/or halogen (to be applied corresponding to any material gas) in the photoconductive layer that is utilized as photosensitive member for electrophotography and formed through the above-mentioned methods is limited as having 10-40 atomic % (U.S. Pat. No. 4,265,991).
Also, when the above-mentioned methods are used to make a total content of hydrogen and/or halogen to 40 atomic % or more by lowering the temperature of a substrate, the resulting photoconductive layer is considerably lower in photosensitivity, and hence cannot be put into practical use for an electrophotographic photosensitive member.
It is expected that the photosensitive member with the conventional a-SiGe photoconductive layer (called hereinafter a-SiGe photosensitive member) could get a higher sensitivity in the longer wavelength range by making smaller an optical band gap in comparison with that of using a-Si not containing Ge, but it has in practice an insufficient photosensitivity, and is smaller in dark resistivity to thereby be notably poor in charge acceptance and dark decay characteristic, so that it is still not enough to be used as a photosensitive member using Carlson process. This may be caused by the fact that a total content of hydrogen and/or halogen in the photoconductive layer is smaller, so that hydrogen and/or halogen are not sufficiently coupled with Ge atom, and hence dangling bonds of the Ge atom itself are is increased. Also, in the case of lowering the temperature of the substrate in the conventional methods in order to increase hydrogen and/or halogen content as mentioned above, the reason why photosensitivity is not sufficient is to be due to the formation of a chain bond of (SiH.sub.2)n.
Under such problems, the present invention intends to provide an electrophotographic photosensitive member which has an improved electric property of photoconductive layer comprising a-SiGe.
In the meantime, it has been proposed to deposit an amorphous silicon film by electron cyclotron resonance method (called hereinafter ECR method). (See U.S. Pat. No. 4,532,199).